IgE-dependent, late phase allergic reactions occur in response to specific allergen exposure, and are characterized by localized leukocyte accumulation. Experiments in this Project will capitalize on recent developments in our understanding of how cytokines, especially TNFa, released by tissue-resident cells, influence pathways critical to cell recruitment to facilitate tissue-specific and leukocyte subtype-specific influx during allergic inflammation. Indeed, studies by our laboratories and others suggest that expression of molecules contributing to selective leukocyte recruitment, such as cell adhesion molecules, chemokines, and eosinophil-activating cytokines, can be dramatically potentiated by TNFa. The central hypothesis of this Project is that TNFa is a powerful amplifier of the allergic inflammatory response, and that its neutralization should lead to a reduction in allergen-induced inflammatory reactions. We also hypothesize that the exact molecular mechanisms involved in these responses depend on the organ involved. This Project, in collaboration with Projects 2, 3 and Core B. will examine mechanisms responsible for experimental allergen-induced inflammation of the skin, nose and lungs. By administering the soluble TNF receptor Etanercept (Enbrel) prior to allergen challenge, we will determine the role of TNFa in late phase reactions. By comparing blood samples to those from nasal or bronchial challenge and lavage, or by comparing biopsies from cutaneous and airway challenge sites in the same subject, Aims 1 and 2 will test the hypotheses that the mechanisms involved in allergen-induced cell trafficking to skin differ from those for the nose and lung, that recruitment of cells at each site involves a defined subset (with respect to adhesion molecules, chemokine receptors, etc.), and that recruitment to all three sites is TNFa dependent. Aim 3 will test the hypothesis that the late phase physiology seen after whole lung allergen challenge in allergic asthmatics is TNFa dependent, as are baseline and allergen-induced changes in airway hyperreactivity. Project 1 will also provide key samples to Project 2 for analysis of basophils and basophil recruitment factors, and to Project 3 for analysis of T cells and accessory cells. This project will improve our understanding of the role of TNFa and other mediators in allergen-induced, tissue-specific cell recruitment responses in humans that may be relevant to allergic disease pathogenesis and treatment.